There are no known systems which provide backward compatibility to the HomePlug® v1.0 system. Background information on the HomePlug® system, which describes the existing system may be found on the HomePlug Powerline Alliance, Inc., website.
U.S. Patent Publication No. 20030156603, of Rakib et al., published Aug. 21, 2003, for Apparatus and method for trellis encoding data for transmission in digital data transmission systems, describes a guard band, or gap, which is reserved for transmission of alignment Barker codes, however, no other data is supposed to be transmitted during the gaps. The guard band is used for a synchronization code for the base station.
EP0622712 B1 of Gee et al., granted Jun. 25, 2003, for Communication network with time coordinated station activity, describes use of a guard band which is located at the end of each periodic interval. When the guard band terminates, a “tone” signal is generated within each node to indicate the temporal boundary between two periodic intervals. Although this signal is not sent over the network, it enables each node to count time in synchronism. An internal tone used for timing in a node is generated but not transmitted.